The attachment of a golf club head to its respective shaft is usually accomplished by the process of adhesive bonding. There are many instances in which the adhesive bond will fail. Adhesives in general tend to weaken with time and with repeated stressing. Constant impact and swing forces tend to repeatedly stress and weaken the shaft/head bond.
Failure of the bond, therefore, becomes inevitable. The club head tends to separate from the shaft at the worst possible moment. That is, failure usually occurs during a swing under maximum separation forces. At the moment of separation, the club head will fly off the shaft, becoming an unguided missile. Therefore, the method of adhesively bonding a club head to its respective shaft creates a potential hazard. Often, reinforcing threads are wound about the shaft at the adhesive juncture. These reinforcing threads also tend to wear and fray with time. Such reinforcement provides little benefit in providing a sound union between the parts.
In copending U.S. patent application Ser. No. 08/831,586, filed on Apr. 9, 1997 and assigned to a common assignee, a process is described for electromagnetically forming a golf shaft over a club head post. The general process of electromagnetically forming is well known, and is illustrated in U.S. Pat. No. 4,523,872 issued to Arena et al, on Jun. 18, 1985, for TORSION RESISTANT GROOVED JOINT. The club head post is contoured so that when the shaft is electromagnetically shrunk upon the surface of the contoured post, an integrally inseparable union is formed therebetween in the vertical direction.
This process provides a strong and permanent bond between the club head of a golf club and its respective shaft. In fact, the actual bonded juncture between the club head and the shaft is actually stronger than the parts themselves.
Some manufacturers prefer that the golf club head be attached to the shaft without the appearance of a connecting process or a joining seam. The seamless process provides an internal bore that runs through the club head completely.
The shaft is inserted into the bore and bonded to the club head by adhesive. Although this type of process may produce a golf club that is aesthetically more pleasing, it nonetheless has the same drawbacks as the other adhesively-bonded shaft and club methods.
The present invention seeks to modify the aforementioned electromagnetic forming process to provide an aesthetic looking, seamlessly-joined golf club.
The method of the current invention includes inserting a hollow, electrically-conductive shaft into a bore hole of a golf club head. Thereafter, a coil of wire is inserted into the hollow shaft and a large electrical current is passed through the coil. The current induces electromagnetic forces to reshape the shaft, so that it expands outwardly into the bore hole of the golf club. The bore hole is fabricated with both longitudinal and circumferential grooves and the shaft fills the contours of these apertures. In so doing, the shaft internally bonds to the club head and is locked in place against both rotational and axial forces. In other words, the shaft is restrained from loosening from the club head due to swing-generated centrifugal forces and impact-generated angular or rotational slippage of the shaft about the vertical axis of the club head post.
In another embodiment of this invention, two counter-sunk depressions are provided in the upper and lower surfaces of the club head. The shaft is outwardly expanded at both counter-sunk surfaces, so that the shaft cannot be withdrawn from the club head in either an upward or downward axial direction along the shaft.